This invention relates to antioxidants which are addition polymerizable.
The demands made on polymeric materials in industrial, commercial and consumer fields are continuously increasing. To improve polymers, the use of antioxidants has been extremely important. Antioxidant formulations currently in use have been developed on an essentially empirical basis by using a limited number of selection procedures. Traditional selection tests, such as the oxygen-absorption test or the oxygen-bomb or air-oven tests may be adequate predictors of antioxidant performance in nondiscriminating applications, but they are quite inadequate under the aggressive conditions often experienced by polymers in modern environments. The ability of an antioxidant to protect polymers under the high-temperature conditions, for instance, of an automobile engine, particularly in contact with fuels or lubricating oils, depends not only on its intrinsic activity, which is adequately reflected by its performance in an oxygen-absorption or oxygen-bomb test, but on its ability to remain in the polymer under these conditions. A similar analysis applies to polymers which are subjected to repeated cleansing operations such as detergent washing or solvent dry cleaning, particularly when they are in the form of articles with a high surface area to volume ratio such as fibers or films.
Three main factors affect antioxidant performance. The first is the intrinsic activity of the antioxidant functional group. This may be evaluated by the induction period of 1-dodecene in a closed system where there is no possibility of loss by volatilization. The second factor is the compatibility or solubility of the antioxidant in the polymer. This second factor is important in situations which are not totally obvious. For instance, a system employing a mixture of two or more polymers may initially have an antioxidant dispersed throughout the system. Upon aging, however, the antioxidant may migrate from one polymer phase to one or more of the other polymer phases, leaving part of the system unprotected. The third factor, discussed above, which is dominant in an open system, is the leaching, or volatility of the antioxidant.
A number of approaches have been tried to solve the problem of the volatilization of antioxidants in polymeric materials. One such approach has been to chemically combine the antioxidant with the polymeric material sought to be protected. Within this approach, several researchers have synthesized antioxidants which have an addition polymerizable double bond. These attempts, however, have not been wholly satisfactory. The polymerizable antioxidants disclosed in the literature are generally expensive to manufacture in that they require synthesis routes which are energy intensive and time consuming. In addition, the products produced by these methods are often inadequate in their ability to function as an antioxidant. Further, the synthesis routes described in the literature generally produce large amounts of impurities, which interfere with the antioxidant properties or other aspects of the polymer system in which they are employed.
Accordingly, it would be desirable to have a polymerizable antioxidant which has a high antioxidant activity, is energy efficient to manufacture, may be quickly and easily manufactured and is relatively free of harmful impurities.